1. Field of the Invention
The present invention relates generally to semiconductor fabrication. More specifically, the present invention relates to endpoint detection during a plasma etching process.
2. Description of the Related Art
In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on semiconductor wafers. The semiconductor wafers include integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials.
The series of manufacturing operations for defining features on the semiconductor wafers can include many processes such as adding, patterning, etching, removing, and polishing, among others, various material layers. Due to the intricate nature of the features defined on the semiconductor wafers, each process is performed in a precisely controlled environment. Furthermore, each process is closely monitored and analyzed to determine an endpoint of the process with exacting precision.
One common manufacturing process is plasma etch. In semiconductor fabrication, plasma etching is commonly used to etch conductive and dielectric materials to define features and structures therein. The plasma etching is typically performed in plasma etch chambers that are capable of etching selected layers deposited over a substrate as defined by a photoresist mask. In general, the plasma etch chamber is configured to generate, confine, and control a plasma by applying radio frequency (RF) power to one or more processing gases contained within the plasma etch chamber. A pressure within the plasma etch chamber is controlled in accordance with a particular desired process. Upon applying the desired RF power, the processing gases within the plasma etch chamber are activated such that a plasma is created. The plasma is configured to perform the desired etching of the selected layers of the semiconductor wafer.
In-situ monitoring and analysis in plasma etching operations can include optical spectrometry. By way of example, optical spectrometry is used to measure properties of plasma optical emissions to provide an endpoint call to a process. The endpoint call is required to be accurate so that an etching process can be stopped once an appropriate amount of material has been removed from the semiconductor wafer.
One problem with current optical spectrometry endpoint detection methods is that the plasma optical emissions are sensitive to changes in the chamber conditions. Thus, changes in the chamber conditions can introduce perturbations in the plasma optical emissions. In some instances these perturbations in the plasma optical emissions can be comparable to an expected perturbation used to trigger an endpoint call, thus causing a false endpoint call to occur.
In view of the foregoing, there is a need for an apparatus and a method to control plasma etching chamber conditions to prevent perturbations in plasma optical emissions that can cause false endpoint detection.